PRESSURE SINTERING, STRUCTURE AND SOME PROPERTIES OF SiC–Al COMPOSITE MATERIALS

Abstract

The pressure sintering of silicon carbide powder mixtures with 15, 30, and 50 wt.% aluminum prepared by grinding in a planetary mill is investigated. A mechanical–chemical synthesis of new Al- and Si-based phases with Fe and O admixtures during grinding is discovered. Further pressure sintering results in the formation of a fine-grained (1–2 m) structure consisting of SiC basic phase, Al and Si oxides, and Al oxysilicide. Oxygen and carbon atoms are uniformly distributed, while Al and Si atoms are concentrated in the structural components of the composites. According to the analysis of compaction kinetics of the composites during non-isothermal reaction pressure sintering, it is found out that their volume flows are controlled by a combination of non-linear creep and linear viscous flow mechanisms, providing the accommodation of the structure of forming phases. These flows are characterized by relatively low activation energies, which can be attributed to the movement of vacancies, when lattice and grain-boundary diffusion. With the exception of SiC–50% Al sintered at 1800 °C, the studied materials are characterized by brittle fracture. The hardness and fracture toughness values of the SiC–Al sintered composites are in agreement with literature data.